A typical wireless communication system is composed of two or more transmitter/receiver nodes adapted to communicate with each other. Communication systems, such as cell phone systems, use frequency, time and code division multiplexing to ensure only a single transmitter is active at any given instant in time (i.e. for a given set of frequencies and codes). To accomplish a message exchange between nodes, each node is adapted to selectively switch between transmit and receive modes by local node control.
Wireless data communications systems, such as conventional radio frequency systems, provide data communications by modulating, or coding, data signals onto a carrier frequency(s). However, other types of wireless communication systems are carrier-less and rely on time-based coding for data communications. One such communication system that relies on time-based coding to achieve reliable data communications is Ultra Wide Band (“UWB”).
These UWB systems, unlike conventional radio frequency communications technology, do not use band-limited carrier frequencies to transport data. Instead UWB systems make use of a wide band energy pulse that transports data using both time-based coding and signal polarization. Time-based coding methods include pulse-position, pulse-rate or pulse-width techniques. By definition, a UWB system does not provide a common clock to the transmitting and receiving nodes. Instead, a low-drift clock is implemented in each transmitter/receiver node, providing a local reference for time-based coding and decoding. Each of these multiple clock domains is subject to short-term time drift, which will exceed the necessary tolerance for accurate UWB system operation after a predictable time period. As a result, precise time synchronization between the transmitting node and receiving node(s) is imperative in UWB systems to obtain accurate data communications. In order to precisely synchronize the receiving node(s) with the transmitting node, UWB systems typically require long preambles for each transmitted data frame. However, some applications with potential to benefit from UWB technology cannot tolerate the elapsed time resulting from preambles at the beginning of each frame or cannot be implemented if a preamble is required. Also, many potential applications for UWB technology are size and energy constrained, such as networks of unattended wireless sensors and controls, which seek to minimize transmission time and to conserve energy.
Existing applications employing UWB technology include short-range radar systems and high speed wireless communications characterized by large amounts of data requiring isochronous signaling, such as real-time voice and video. Generally, the signal used for a UWB application requires a preamble at the beginning of each transmitted frame to enable a receiver(s) to synchronize with the time-based coding being transmitted. The time required for transmitting the preamble, and subsequent data, imposes a minimum time between reversals in the direction of data communications between two transmitter/receiver nodes in a UWB system, which in turn restricts the scope of applications suitable for UWB implementation. Also, the energy consumed to transmit the preamble for existing applications is a significant fraction of the overall energy required to transmit the preamble and subsequent data.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the communication industries for a method to provide collaboration among two or more transmitter/receiver nodes that eliminates multiple re-synchronization preambles and minimizes energy consumption at each node.